Field of the Invention
The present invention relates to a fixing device included in an image forming apparatus, such as a copier or a laser-beam printer, employing an electrophotographic image forming process.
Description of the Related Art
Some known fixing devices included in electrophotographic image forming apparatuses employ films. Such a fixing device includes a tubular film and a heater provided in contact with the inner surface of the film, and fixes a toner image on a recording material by utilizing the heat of the film.
The film employed by the fixing device has a small heat capacity. Therefore it is known that, if recording materials of small sizes are successively subjected to the fixing process, the temperature in a non-sheet-passing area where the recoding materials do not pass tends to rise excessively. Hence, in a fixing device disclosed by Japanese Patent Laid-Open No. 11-84919, a metal plate is provided between a heater and a supporting member so that the heat in a non-sheet-passing area is diffused by the metal plate, whereby the excessive rise of the temperature in the non-sheet-passing area is suppressed.
The fixing device disclosed by Japanese Patent Laid-Open No. 11-84919, however, has a problem in that the heat of the heater tends to be transferred to the supporting member through the metal plate and, consequently, the warm-up time of the fixing device increases. Accordingly, the present invention provides a fixing device in which the excessive rise of the temperature in the non-sheet-passing area is suppressed while a short warm-up time is realized.